SearchAttributeTag null pointer exception

Hello!

I'm developing some code. On it, im trying to set the display values of a SearchAttributeGroup object depending on the value previously selected in a SearchObjectTypeDropDownList. This is my code (the in variable type_name is the type selected in the dropdown list):

private void setSelectSearchAttributeGroupTypes(String type_name) throws Exception {

IDfSession session;

try {

createSessionManager("MyRep","dmadmin","admin");

session = sMgr.getSession("MyRep");

IDfQuery query = clientx.getQuery();

query.setDQL("select * from dmi_dd_attr_info where type_name='"+type_name+"'");

IDfCollection col = query.execute(session,DfQuery.DF_READ_QUERY);

SearchAttributeGroup attgSelectTypes= (SearchAttributeGroup)getControl("attributesearchcriteria",SearchAttributeGroup.class);

attgSelectTypes.clear();

while (col.next()){

SearchAttributeTag tag=new SearchAttributeTag();

tag.setAttribute(col.getString("attr_name"));

attgSelectTypes.addSelectableSearchAttribute(tag); (AdvSearchExArogestion.java:204)

}

col.close();

clientx = null;

sMgr = null;

} catch (Exception ex) {

throw ex;

}

But I get the following error:

java.lang.NullPointerException

at com.documentum.web.form.BodyControlTag.getForm(BodyControlTag.java:324)

at com.documentum.web.form.BodyControlTag.createControl(BodyControlTag.java:337)

at com.documentum.web.form.BodyControlTag.getControl(BodyControlTag.java:410)

at com.documentum.web.formext.control.docbase.search.SearchAttributeGroup.addSelectableSearchAttribute(SearchAttributeGroup.java:296)

at com.emc.xcelerator.advsearch.AdvSearchEx.setSelectSearchAttributeGroupTypes(AdvSearchEx.java:204)

at com.emc.xcelerator.advsearch.AdvSearchEx.selectSearchAttributeGroupTypes(AdvSearchEx.java:232) (The call to the setSelectSearchAttributeGroupTypes method)